Security system and lock

Abstract

A code system comprising a temperature-resistance conversion element the change of electric resistance value of which describes a hysteresis loop with respect to a temperature change; a means for changing the temperature of said temperature-resistance conversion element; a means for detecting the change of the electric resistance of said conversion element; and a time counting means of counting the actuation time of said temperature changing means. A hard lock device for use in the code system is also disclosed.

What is claimed is: 
     
       1. A security system, comprising: (a) a temperature-resistance conversion element having a hysteresis loop characteristic which exhibits a peak electrical resistance at a peak time after the temperature of the element has been raised and then lowered;   (b) temperature changing means operative from a start time for raising and then lowering the temperature of the element to generate the peak electrical resistance;   (c) means for detecting the generation of the peak electrical resistance;   (d) timing means responsive to the detecting means, for measuring a time interval between the start time and the peak time; and   (e) control means responsive to the timing means, for generating a security signal when the time interval lies within a predetermined range.   
     
     
       2. The security system as recited in claim 1, wherein the conversion element is a thermo-elastic martensite transformation alloy. 
     
     
       3. The security system as recited in claim 1, wherein the temperature changing means heats the element and, in turn, increases the resistance from a heat value of resistance to a second value of resistance, said second value of resistance being lower than said peak resistance; and wherein the temperature changing means stops heating the element at a stop time after which the resistance initially decreases in value, then at the peak time increases to the peak electrical resistance, and thereafter decreases in value. 
     
     
       4. The security system as recited in claim 1, wherein said hysteresis loop characteristic is a closed loop having more than one value of resistance for a given temperature. 
     
     
       5. The security system as recited in claim 1, wherein said temperature changing means includes means for applying a voltage having a first amplitude during the raising of the temperature of the element, and for applying a voltage having a second amplitude during the lowering of the temperature of the element, said second amplitude being less than said first amplitude. 
     
     
       6. The security system as recited in claim 1, wherein said temperature changing means includes a heater in thermal communication with the element. 
     
     
       7. The security system as recited in claim 6, wherein said heater is an induction heater. 
     
     
       8. The security system as recited in claim 1, wherein said detecting means includes means for connecting the element to an electrical circuit connected to a voltage supply, and means for detecting a peak voltage corresponding to the peak resistance. 
     
     
       9. The security system as recited in claim 1, wherein said detecting means includes means for connecting the element to an electrical circuit connected to a voltage supply, and means for detecting a minimum of electrical current corresponding to the peak resistance. 
     
     
       10. The security system as recited in claim 1, wherein said detecting means is located out of physical contact with the element. 
     
     
       11. The security system as recited in claim 10, wherein said temperature changing means is operative to generate eddy currents in the elements, and wherein the detecting means is operative to detect a change in the eddy currents upon the generation of the peak resistance. 
     
     
       12. The security system as recited in claim 1, wherein said timing means includes a clock connected to the temperature changing means, the detecting means and the control means. 
     
     
       13. The security system as recited in claim 1, wherein said control means has an actuatable input to which a code signal is supplied, and an output from which the security signal is supplied. 
     
     
       14. The security system as recited in claim 1, and further comprising a support on which the conversion element is supported, said support maintaining its shape during operation of the temperature changing means. 
     
     
       15. The security system as recited in claim 1, wherein said support is a planar sheet. 
     
     
       16. A lock for use in a security system, comprising: (a) a temperature-resistance conversion element having a hysteresis loop characteristic which exhibits a peak electrical resistance at a peak time after the temperature of the element has been raised and then lowered; and   (b) a support on which the conversion element is supported, said support maintaining its shape during the change in temperature of the element.